The present invention relates to a method and apparatus for increasing the volume of tobacco, especially for increasing the volume of tobacco ribs and stem.
It is already known to increase the volume of tobacco particles, expecially tobacco ribs, by resort to a variety of wetting, heating and drying techniques. U.S. Pat. No. 3,734,104 discloses a method which involves heating tobacco whose moisture content is very high. The heating step entails evaporation of moisture in the interior and the resultant expansion or puffing of the particles of tobacco. U.S. Pat. No. 4,289,148 proposes to contact tobacco particles with a compressed inert gas so that the gas penetrates into the particles of tobacco. The pressure of gas is thereupon relaxed and the particles of tobacco are heated, e.g., by resort to microwaves. U.S. Pat. No. 4,250,898 proposes to contact the particles of tobacco with carbon dioxide at a relatively low pressure whereby the gas penetrates into the particles. This step is followed by rapid cooling which entails condensation and crystallizing of carbon dioxide in the particles of tobacco. The cooling step is followed by heating which results in expansion of tobacco particles and expulsion of carbon dioxide.
It is further known to subject tobacco ribs to a highly intensive moisturizing action so that they undergo pronounced swelling. The thus swollen particles of tobacco are thereupon contacted by a hot air stream for a short interval of time whereby the air stream solidifies the outermost strata of tobacco particles and stabilizes the shape of expanded material (reference may be had to British Pat. No. 1,290,613). British Pat. No. 1,381,203 discloses the introduction of moist tobacco into a chamber and rapid evacuation of (i.e., reduction of pressure in) the chamber.
A drawback of the above outlined and other prior proposals is that the cost of expanding the volume of tobacco particles is very high, that the increase of volume is relatively small so that it does not warrant the expenditures which are involved in achieving such minor increase of the volume, and/or that the throughput of the apparatus which is used for the practice of conventional methods is low or very low.